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The Heart of Darkness:

The Heart of Darkness:. Josh Simon and Josh Adams Carnegie Observatories. The Dark Matter Density Profiles of Dwarf Galaxies. Cusp/Core Problem. L CDM predicts steep central density profiles. cusp vs. core. Navarro, Frenk, & White (1996). Cusp/Core Problem.

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The Heart of Darkness:

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  1. The Heart of Darkness: Josh Simon and Josh Adams Carnegie Observatories The Dark Matter Density Profiles of Dwarf Galaxies

  2. Cusp/Core Problem • LCDM predicts steep central density profiles cusp vs. core Navarro, Frenk, & White (1996)

  3. Cusp/Core Problem • If you parameterize density profile as r(r) µ r –a • Observations show a ~ 0 (constant-density core) • Simulations predict 1 a 1.5 (central cusp)

  4. Cusp/Core Problem • If you parameterize density profile as r(r) µ r –a • Observations show a ~ 0 (constant-density core) • Simulations predict 1 a 1.5 (central cusp) Navarro, Frenk, & White (2008)

  5. Previous Results • Large samples of H and HI rotation curves (e.g., de Blok et al. 2001; Gentile et al. 2004; Kuzio de Naray et al. 2006, 2008; Oh et al. 2011) • Typically find very shallow density profiles: a = 0.2 ± 0.2 Simon et al. (2003) Oh et al. (2011)

  6. State of the Field • What we know: • Gas velocity fields are on average fit by density profiles shallower than NFW

  7. State of the Field • What we know: • Gas velocity fields are on average fit by density profiles shallower than NFW Simon et al. (2005)

  8. State of the Field • What we know: • Gas velocity fields are on average fit by density profiles shallower than NFW • What we don’t know: • Do these velocity fields accurately trace the galactic potential?

  9. What We Are Doing Differently • Stellar kinematics • collisionless tracer • no non-gravitational forces • VIRUS-W IFU • 0.9’ x 1.8’ FOV • R ~ 8000 • 267 3” fibers Fabriciuset al. (2008)

  10. Example VIRUS-P data (NGC 2976) 18 hours of data: Ca H/K G band [OII] 3.3 kpc Balmer series

  11. NGC 2976 Velocity field Velocity dispersion km s-1 km s-1 arcsec arcsec Adamset al. (2012)

  12. Kinematic Modeling • Multiple Gaussian Expansion (MGE) and Jeans Anisotropic Modeling (JAM) (Cappellari 2008) • Can fit either power-law DM profile (as for NGC 2976) or generalized NFW: • Other free parameters: M*/L, bz Adamset al. (2012)

  13. JAM models and mass profiles Observed 2nd moment map Best cuspy model Best cored model (α = 0.1) SED fits give ¡*,R = 1.1 ± 0.8, so a= 0.9 ± 0.3 α ¡*,R Adamset al. (2012)

  14. JAM model residuals Observed uncertainty map Best cuspy model Best cored model (α = 0.1) • Stellar kinematics disfavor a core at ~2s • Gas kinematics find a robust core (a = 0.01 ± 0.13) Simon et al. (2003) Adamset al. (2012)

  15. NGC 959 Velocity field Velocity dispersion field • Halo is cuspy independent of M*/L • Gas kinematics prefer a core Adamset al., in prep

  16. NGC 2552 Velocity field Velocity dispersion field Velocity dispersion residuals • Best fit has a = 0 • Low concentration cuspy model also allowed with slightly larger residuals Adamset al., in prep

  17. More Data to Come . . .

  18. Summary • With new IFUs, can determine density profiles from stellar kinematics • Degeneracy between baryons and dark matter can be broken with a stellar pop constraint • Some galaxies whose gas kinematics indicate cores now appear to have cusps • Gas results may be more model-dependent, but can be made compatible with cuspy profiles

  19. VIRUS-P and VIRUS-W Properties • VIRUS Prototype IFU • 1.’6x1.’6 FOV at HJST • Largest FOV of any existing IFU • 4.2’’ diameter fibers on sky • 3680-4400Å • R~2400 (inst~50 km/s) • VIRUS Wendelstein IFU • Made by Maximilian Fabricius (MPE) • 0.'9x1.'8 FOV at HJST • 3.1” diameter fibers • 4800-5400Å • R~8300 (inst~18 km/s)

  20. A VIRUS-W LOSVD Essential to have K giants and hot (A or B) dwarfs to match EWs

  21. Reconciling the two tracers Solid line from best JAM model Left: tilted ring with variable PA Middle: harmonic decomp. Right: Simon '03 data and harmonic decomposition

  22. Parameter constraints UGC 2002 (preliminary)

  23. *,R Constraint • Two stellar population fits • Used the Tremonti et al. (’04) Z and SFH grids • Used (BC03,BC07) and (Chabrier,Salpeter) IMFs • Used Calzetti et al. ’00 dust law • Fit all two-population combinations • BC03 Salpeter: *,R=1.23±0.52 • BC03 Chabrier: *,R=0.63±0.39 • BC07 Salpeter: *,R=1.42±0.42 • BC07 Chabrier: *,R=1.04±0.23 • Total is *,R=1.1±0.80

  24. *,R Constraint

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